Spray gun for electrostatic spray coating of objects

Abstract: Spray gun for electrostatic spray coating of objects, namely for a powder coating material, comprising a gun barrel (1) including a high voltage generator, topped in a replaceable nozzle (2), and a grip or support member (10, 11), a duct (14) for the coating material circulation, extending along said barrel and grip or support, and electrodes (17) connected to said high voltage generator and interposed to the passage of the product to spray. According to the invention the spray gun is composed of a tubular element (6), acting as support of the barrel body (1), said element (6) being laterally extended by a portion (7) continued by a grip (10) or a supporting member (11) fastened to an automatic handler member, and said element (6) receiving, tightly inserted, a rear part (5) of the barrel (1), of smaller section, lengthwise delimited by a step (18) and topped by an end configuration (19) adapted to fasten a detachable part (8) which keeps linked the two bodies support (6) and barrel (1). The tubular support section comprises some passages to insert therethrough some ducts (16, 46) to supply powder and fluid and electrical current.

Description: This invention relates to a spray gun for electrostatic spray coating, namely for a powder coating material, of the type which comprises a gun barrel ended in a replaceable nozzle, and a grip or supporting member, whose barrel gun integrates a high voltage generator, constituted by a voltage multiplying circuit and a transformer, and a duct, generally axial, for the coating material circulation, a material such as powder paint driven by a pressurized fluid, which extends along said gun barrel and grip or support, formed by several coupled tubular lengths, which may be detached and replaceable, to make production tasks easier (more plain molding of the gun body in electrically insulating material), cleaning, servicing and repair and, namely making easier the change of colour of the paint used, said spray gun embodying likewise electrodes connected to said high voltage generator and interposed to the passage of the product to spray. A gun of said characteristics appears disclosed in the utility model n º 264,765 owned by the applicant, whose main and more significant characteristic lays in allowing a quick mounting and dismounting, with the possibility of replacing the main elements should any fault arise. For such aim, in said gun, an assembly is proposed wherein the voltage multiplying circuit and the transformer are formed by means of modules which are independent and replaceable, which are housed in the interior of a tubular body or housing which constitutes the gun barrel. The duct for impelling the powder may likewise be detached and is formed of two replaceable tubular elements, which are coupled through an elbow which extends along said gun barrel and the grip, respectively. Although the solution proposed in said utility model is effective, bearing in mind that the voltage multiplying circuit is constituted by an insulating cylindric block which is axially socketed in a housing of the housing-barrel, stopping in an end narrowing of said housing through which it sets an electrical connection by means of contact stems with the electrodes, it results that in said connection area as the air always remains trapped and because of the high voltage existing there, there is the risk that said contact stems are corroded, with a further defaulting passage of the current (sparkling) which, with time can cause that the electrically insulating housing has a hole, of a smaller thickness at such end part of the barrel, setting the assembly out of order. On the other hand, in the EP-A 0110753, improvements are proposed in the electrostatic guns which aims to be able to combine the type of hand gun with the one used in automatic devices, by the exchange of one part of the gun to obtain a gun having a grip or a supporting member, the rest of the gun being common for both types. For such aim, in said patent it is proposed to constitute the gun with a first part having the shape of a grip or supporting member comprising same elements: oscillating circuit, transformer and means for connection of an oscillating circuit to an external power supply and the connection means of the duct for the passage of the coating material impelled by pressurized air to a particle feeding external device, and to a second part which comprises the barrel with the voltage multiplying circuit, the electrodes and the spraying nozzle, said two parts being mechanically and electrically connected to constitute an operating assembly. This structure despite it offers good performances, has same risks as those appearing in mentioned utility model, when establishing electrical connection between the two bodies from the outlet of the transformer with voltages ranging around 3,500 V, demanding significant insulating material thicknesses surrounding the electrical union connectors with the voltage multiplying circuit and on the other hand it has a lower modularity of the components integrating them, with respect to the solution disclosed in mentioned utility model n º 264,765. This invention tries to eliminate the drawbacks of above disclosed guns and for such aim, it proposes an execution of at least the voltage multiplying circuit and, in general, also of the transformer, forming a whole, embedded within an insulating material block constituting the barrel and whose block is detachably related to a body acting as a support, which is extended in a portion having the shape of a grip or of a supporting member. More concretely, the gun for electrostatic spray object of the invention including all the features of mentioned EP-A-110753 according to the preamble of claim 1 is characterized in that it includes a tubular section element, acting as support of the barrel, which is laterally extended in a portion which continues in turn adopting the shape of a grip or like a supporting member to an automatic handler element, said tubular section element being designed to receive tightly inserted only a rear part of the barrel, having a slightly smaller section, lengthwise delimited by an annular step and ended by an end configuration adapted to allow to fasten a detachable part which keeps linked the two barrel and support bodies. Said tubular section element has at its lateral extension portion, passageways for arranging through them the ducts of air and powder circulation, low voltage supply to the transformer and an additional air flow. This way, an assembly having similar performances as the electrostatic spraying guns disclosed in the utility model n º 264,765 and EP-A-0110753 is achieved, but with a different structure and interrelation between the sub-assemblies forming thereof, which guarantees a much longer working life as no free inter-spaces exist with air trapped between the high voltage units and providing best coupling conditions of said sub-assemblies which make the replacement of one part of the pistol easier, its easy adaptation to a hand or an automatic handling and an uncomplicated access to any of the components, for its servicing or replacement. In addition, the tubular section element acting as support is a part easy to produce and the mounting tasks of the gun are easy and can be quickly achieved. To best understand the characteristics of the object of the invention this later will be disclosed with the help of the attached drawing sheets wherein it has been shown the following: Fig. 1 is a perspective partial view of one of the component parts of the gun, illustrating the principles on which the invention lays. Fig. 2 is an elevation view of a lengthwise section of a hand gun constructed according to the invention, showing the whole of its component parts as well as their functional interrelation. Figure 3 shows a partial lengthwise section of an electrostatic spray gun for an automatic handler, constructed according to the principles of the invention. Fig. 4 shows an embodiment of execution of the spray replaceable nozzle , ending the gun according to the invention. As it is shown in figure 1, the disclosed electrostatic spray gun is composed of a tubular section element -6-, acting as support of the barrel body -1- which laterally extends in a portion -7- which, in turn, is continued by a grip -10- (figure 2) or in a supporting member -11- (figure 3) fastened to an automatic handler member not represented and said tubular section element -6-receives , tightly set, a rear part --5- of the barrel, having a slightly smaller section, lengthwise delimited by an annular step -18- and topped by an end configuration -19- adapted to allow fastening a detachable part -8- which keeps linked the two bodies support and barrel as shown in figures 2 and 3. The barrel body -1- is ended at its front part in a nozzle -2- having a spray oblong hole -3-, locked by a threaded sleeve -4-, and said barrel houses, embedded within its body, formed by an insulating material block, a high voltage generator which comprises a voltage multiplying circuit -12- and a transformer -13- around a centering core -29-, and a duct -14- for the circulation of the coating material impelled by a fluid such as pressurized air, which axially extends along said barrel -1- and the grip -10- or supporting member -11-, and an electrode -17- interposed to the passage of the product to electrostatically spray and which is protruding at the front end of the nozzle -2-. The duct -14- is formed by two lengths -15- and -16- detachable and replaceable associated to an elbow -28- fixed in the interior of the body -1- and supported by a block -27- according to the well known structure disclosed in the mentioned utility model n º 264,765. On its side, the voltage multiplying circuit -12-is electrically connected through an electric conductor -45-, resistor -30- and a connector-stem -32- which crosses a ring -31- auxiliary to an electrode -17- located within an hollow rod -33-, locked by a ring -37- and with a sealing gasket -38-, said rod -33- bearing the electrode possesses at its end part a centering socket -43- in electrically insulating material. The hollow rod -33- shows at a base portion a first radial duct -35- for the passage of an electric conductor which connects the connector -32-to the electrode -17- and a second duct -36- to which converges a duct -21- having a smaller passage than the -14- for circulation of coating material and impelling fluid, for the circulation of an additional air flow. This way and through said duct -21- an air flow can be sent to the interior of the hollow rod, i.e. to a duct -34- which surrounds the electrode -17- forming an ionized air flow. Said duct -21- comprises a first length -22- which spreads along the barrel and is continued by a length -23-, advantageously flexible, adapted to pass through the grip -10- section (locked to the grip by a clamp -26-) or through the supporting member -11-, by suitable passageways arranged at the portion -7- which laterally extends the tubular section element -6-, making the dismounting of the body -1- easier. This duct --21- can be formed as well as the duct -14- by several coupled, dismountable lengths, associated to a connecting elbow -27- set within the body -1-. The rear portion of the barrel comprises a cylindric terminal part -19- having a smaller section, which is internally threaded and the part -8- which keeps the two support -6- and barrel -1- bodies is formed by a plug having an externally threaded core -9- (see figure 1) which is inserted threaded in said portion -19- and is, in turn, introduced in the mouthpiece of the tubular section element -6-, embodying a perimetral flange -20- which rests against the end of said tubular section element -6-, linking it to the barrel body -1-. As it is shown in figures 2 and 3, the height of the step -18- which delimitates the rear portion -5- of the barrel -1- inserted in the tubular section element -6- is coincident with the thickness of its wall, in such a way that the surface of the front part of the barrel -1-remains level with the surface of the support tubular element -6-. As it can be seen in figure 2, it is also a characteristic of the invention that the grip -10- section comprises a front portion -24- corresponding to the part where the push-button -25- or driving latch is mounted, which is constituted by a part detachably linked to the sides of the grip -10-, by locking means -39- ( screws and nuts), adapted to be coupled with tongues and grooves with the rest of the grip, allowing a direct access to the interior of said grip -10-, the tasks or servicing, repair, withdrawal and replacement of the tube -16- etc. are so made easier. Also and in the example of embodiment of the figure 2, it is shown that the support tubular element -6- of the barrel -1- shows at its higher part, near to its back, an appendage hook-shaped -47-, to hang the gun. The embodiment illustrated in the figure 4 only differs from the example of the figure 2 by the use of a different nozzle -41-, ended in a circular opening embodying a deflector -42- associated with possibility of lengthwise setting to the end of the hollow rod -33-, axially to which spreads the electrode -17- for the electrostatic loading of the particles. On its side, in the embodiment shown in the figure 3 the holes -40- are seen to lock such supporting member to an automatic handling tool. In any of the embodiments, the tubular section element -6-, will show a passageway -45- for the arrangement through it of a power supply cable -46- which continues by the conductor -44- up to the transformer -13-, which possesses a centering central core -29-. In an alternative embodiment the barrel may include only embedded in its body the voltage multiplying circuit -12-, while the transformer -13- can be constituted by a module which can be coupled to a socket-outlet in the interior of a housing of the barrel and connectable to said circuit -13-, bearing in mind that the outlet voltage of this transformer of about 3500 V in said area, having a significant thickness of the wall, is less critical than in other zones of the spray gun.

Claims: Spray gun for electrostatic spray coating of objects, namely for a powder coating material, of the type which comprises a gun barrel (1) ended in a replaceable nozzle (2), and a grip or support (10, 11), whose barrel gun includes a high voltage generator, constituted by a voltage multiplying circuit (12) and a transformer, and a duct (14), generally axial, for the coating material circulation, a material such as powder paint driven by a pressurized fluid, which extends along said gun barrel and grip or support, formed by several coupled tubular lengths (15, 16), which may be detached and replaceable, and some electrodes (17) connected to said high voltage generator and interposed to the passage of the product to spray, characterized in that the spray gun is composed of a tubular section element (6), acting as support of the barrel body (1) which laterally extends in a portion (7) which, in turn, is continued by a grip (10) or in a supporting member (11) fastened to an automatic handler member, said tubular section element (6) receiving , tightly set, a rear part (5) of the barrel (1), having a slightly smaller section, lengthwise delimited by an annular step (18) and topped by an end configuration (19) adapted to allow fastening a detachable part (8) which keeps linked the two bodies tubular section element (6) and barrel (1), said tubular section element comprising some passages to insert therethrough some ducts to supply powder and fluid (16), and electrical current (46) Spray gun, according to claim 1, characterized in that the rear portion (5) of the barrel (1) comprises a cylindric terminal part (19) having a smaller section, which is internally threaded and the part (8) which keeps the two tubular section element (6) and barrel (1) bodies is formed by a plug (8) having an externally threaded core (9) which is threaded inserted in said portion (19) and is, in turn, introduced in the mouthpiece of the tubular section element (6), said part (8) embodying a perimetral flange (20) which rests against the end of said tubular section element (6), linking it to the barrel body (1). Spray gun, according to claim 1, characterized in that the height of the step (18) which delimitates the rear portion (5) of the barrel (1) inserted in the tubular section element (6) is coincident with the thickness of its wall, in such a way that the surface of the front part of the barrel (1) remains level with the surface of said tubular support. Spray gun, according to claim 1, characterized in that the voltage multiplying circuit (12) and the transformer (13) are both embedded in an electrically-insulant block constituting the barrel body (1). Spray gun, according to claim 1, characterized in that it includes a duct (21) having a smaller passage than the one (14) for circulation of coating material and impelling fluid, for the circulation of an additional air flow towards a zone located at the front end of the barrel (1) where an electrode (17) is placed, said duct (21) being constituted by a tubular element (22) extending along the barrel (1) and which is prolonged by a length (23) which can be able to pass through the grip section (10) or supporting member (11). Spray gun, according to claim 5, characterized in that the length (23) is constituted by a flexible duct. Spray gun, according to claim 5, characterized in that the length (23) is constituted by an exchangeable duct which is coupled to the tubular element (22) by an elbowed member . Spray gun, according to claim 1, characterized in that the grip (10) section comprises a front portion (24) corresponding to the part where the push-button (25) or driving latch is mounted, which is constituted by a part detachably linked to the sides of the grip (10), by locking means (39) adapted to be coupled with tongues and grooves with the rest of the grip (10). Spray gun, according to claim 1, characterized in that the tubular section element (6) of the barrel (1) has at its higher part, near to its back, an appendage hook-shaped (47), to hang the gun.

Inventors: DE FUSCO LUPO JOSE, DE FUSCO LUPO, JOSE, De Fusco Lupo, José
Applicants: FUSCO LUPO JOSE DE, DE FUSCO LUPO, JOSE
Application year: 1994
Main classification: B05B5
IPC codes: B05B5